This type of semiconductor device is required to reduce gate capacitance in order to increase the switching speed. Because the gate capacitance increases in proportion to the number of gate electrodes, reduction of the gate capacitance can be realized by reducing the number of gate electrodes. However, simply reducing the number of gate electrodes disturbs the potential distribution in the semiconductor device when the semiconductor device is turned off, reducing the withstand voltage of the semiconductor device. For this reason, Japanese Patent Application Publication No. 2002-353456 proposes the following technology.
The semiconductor device disclosed in Japanese Patent Application Publication No. 2002-353456 is provided with first and second trenches that penetrate a body region from an upper surface of a semiconductor substrate to reach a drift region. A gate electrode that is insulated from an emitter electrode is formed inside the first trench. A polysilicon region that is electrically connected with the emitter electrode is formed inside the second trench. Because there are no gate electrodes formed in the second trench of this semiconductor device, the number of gate electrodes can be reduced. Therefore, reduction of gate capacitance can be achieved in this semiconductor device. In addition, because the polysilicon region of the second trench is electrically connected with the emitter electrode, the same potential as that for the emitter electrode is applied to the polysilicon region. Thus, when the semiconductor device is turned off, the polysilicon region of the second trench is applied with the same potential as that of the gate electrode, preventing the potential distribution in the semiconductor device from being disturbed. As a result, the decline of the withstand voltage of the semiconductor device is prevented.